Casio produced their first scientific calculator watch in 1983, the CFX-20 (resin case) and CFX-200 (metal case) which, while getting rarer and more expensive, can still be found in varying condition on eBay without looking too hard.
Then, in 1984 or 1985, they started producing watches with a membrane keypad, including databanks like the DBC-60/600, the thin CFS-80, accountant’s friend CBA-10 and, unfortunately, the updated scientific calculator watches CFX-40 (resin case) and CFX-400 (metal case).
The calculator watches with buttons that sat proud of the keypad, that had served them so well for five years across a range of different models including the original CFX watches, were far better than this replacement keypad that faded and cracked with use.
As a result, the CFX-40/400 is a real rarity in any condition, particularly if you’re seeking one with a usable keypad.
Some enthusiastic designers have come up with a partial workaround, producing replacement vinyl adhesive keypads to stick over the old ones but they don’t quite match the originals and are, themselves, quite fragile. Much like the after-market G-Shock bezels being produced in China and Brazil, they look good from a distance but not on closer inspection. However, they are definitely better than nothing.
The watch pictured here started life as a CFX-40 but the keypad had cracked and the numbers all but disappeared. The seller said it was worse before he had given the keypad a cursory spit and polish and, while it was able to be coaxed back into life, it’s pretty much unusable other than a basic 8-digit calculator if you can’t see the other symbols on the keys.
NOS cases appear on eBay very rarely and are quickly snapped up so I wasn’t particularly confident when putting out some feelers to see if I could find a replacement — I was quite sure the best I’d be able to find was one of the after-market vinyl keypad overlays.
But, occasionally miracles happen, and a Spanish seller had a NOS case for a CFX-400 with the white/yellow keypad. More incredible still he had a NOS black keypad as well which he bundled with it. Overall it was an expensive transaction, but the chances of finding another are not great so worth every cent.
Those familiar with the CFX-400 will be well-aware of the range of available functions it holds, and for mathematicians, engineers, and people who just like doing calculations in baseⁿ it’s in a class of its own. Other than the CFX-20/200 and a scientific calculator watch Citizen made, there’s nothing else like it. It’s features seem to parallel the widely-popular desktop calculator Casio FX-82, but having it on our wrist adds another dimension.
Obviously with the invention of smart watches, having a wristwatch calculator is not only possible, but has far more functionality than this. But the CFX-400 was made more than 30 years ago.
An excellent watch, well-deserving of the high prices good examples command on eBay.
Here’s the CFX-40 and 400 from the 1985 Casio catalogue, along with 1983’s CFX-200, the thin CFS-80 and two of the many QW437 variations, the CA-50 and CA-502.
Interestingly, the catalog has the CFX-400 with a very white keypad — I’ve never seen a real one with a keypad this white and even NOS ‘white’ keypads tend to have a yellow tint. The stark white looks very nice though and blends well with the silver case.